Aims: In this study, the effectiveness of chitosan as a coagulant aid in the removal of turbidity from surface water was investigated. Materials and Methods: A conventional jar test apparatus was used to evaluate the coagulation process. Coagulation of turbidity in river water using chitosan as coagulant aid and ferric chloride as coagulant was studied in the pH range 4-9 and initial turbidity concentrations in the range of 20-200 mg/l. Results: The findings showed that the optimum pH for FeCl 3 as a coagulant on turbidity removal was seven. About 95% removal of turbidity is achieved at this pH, without filtration and the residual turbidity drops below 5 NTU. The optimum dosage of FeCl 3 was achieved 10 mg/l. The optimal chitosan concentration required to effect coagulation is 0.5 mg/l. Restabilization of the turbidity is observed at higher concentrations of chitosan. When chitosan (0.5 mg/l) used as a coagulant aid, efficiency removal turbidity was increased and optimal dosage of FeCl 3 turbidity removal was reduced to 50% of initial dosage of FeCl 3 . Conclusion: Chitosan as natural coagulant aid improved turbidity removal efficiency by coagulation process. And FeCl 3 concentration as coagulant was reduced then residual iron decreased in treated water. Also by using natural coagulant considerable savings in chemicals and sludge handling cost may be achieved.